As Kerala grapples with the aftermath of unprecedented rains and inundation, Secretary, Ministry of Earth Sciences M. Rajeevan explained the challenges of forecasting floods in the State with relatively small rivers prone to flash floods, inaction at the local level despite meteorological alerts and dam management.
In terms of modelling, how well did our rain forecast models capture the possibility of such heavy rains in Kerala?
As far as Kerala is concerned, in August we had two spells — on the 4th and the 14th — and both of these were captured by our short range weather prediction system. Each of them were forecast three days in advance. We give a forecast for heavy rains district-wise — in the form of orange and red alerts. I’d checked it today and the India Meteorological Department has prepared a map showing the districts — particularly hilly regions like Idukki, Wayanad — where the alert was given two-to-three days in advance.
But did these maps give an estimate of the quantum of rains expected — after all rains were on average 50% and some places double the normal?
A ‘red alert’ means that you must initiate action. It means that the IMD is expecting heavy rains, so State officials shouldn’t just be waiting.
Typically our authorities don’t take immediate action based on a red alert alone...?
That’s a different issue but from the IMD’s side, we’ve already warned. An ‘orange’ means ‘be on alert’ and a ‘red’ means take action. So for instance, if a dam is full and you’ve been warned of heavy rains, then that means you should have been careful. Unfortunately, I’ve been given to understand that Kerala has no flood warning system. The Central Water Commission (CWC) doesn’t have a flood warning station in Kerala.
But they do monitor rivers and the water levels in rivers…
In Kerala the rivers are relatively small. For instance, if it rains in a hilly region, it can flood within 25 minutes and in an hour, the water will come. Rivers like Cauvery and Narmada have huge basins and such inundations are much slower.
Is there any reason there’s no flood warning system in Kerala?
Well, it’s said that this kind of a calamity hasn’t happened in the past anywhere. As I said, the focus [by the CWC] is on large rivers and especially those that traverse multiple States. The point is that, any river can be flooded and any place can be flooded.
But from the earth sciences perspective, can’t these flows be observed via satellites and forecasts prepared? You use them for studying the oceans…
Frankly speaking, we don’t have the mandate. This is entrusted to the CWC. We (IMD) have 11 flood warning offices such as in Ahmedabad, Bhubaneshwar etc.. They interact with the CWC everyday during the monsoon. Every river is divided into basins and we give a two-to-three day forecast for each basin and we give a quantity — the average rainfall over the basin and how much is likely — and we run them in weather models to generate a forecast. This is given to CWC and they in turn use it to estimate how much water is likely in a river. I understand that now they give such forecasts, five days in advance. We unfortunately don’t have such a system in Kerala.
Now might be a good time to establish one…
Unfortunately the lead time would still be short…a river can flood in half-hour. We can also use radars… during all this time, we have a radar in Thiruvananthapuram and Kochi. Our local meteorology offices there used to give CWC ‘nowcasts’ (forecasts valid for two hours). This is based on how convective clouds form and the way they move. All these products are being given.
However they have to be intelligently used by the recipient. I’m not blaming individuals, institutions or government but it’s a fact that in India, none of our reservoirs are managed using a scientific, decision-support system. It’s left to a few individuals to take a decision. A good example was the Surat floods in 2006 — it happened because somebody just decided to open a shutter. Or the Bihar floods…
Is it because reservoirs are the property of States and managed entirely by them?
Dams are managed by States and they worry about their own personal requirements such as, hydro-power management. You should know that (in the case of Kerala this year) it’s July, the dams are full, there are two months of monsoon left…I’ll stop at that and don’t want to interpret further. Decisions should be made by talking to the meteorological office, factoring inputs. I don’t think there’s such a mechanism in place.
When the monsoon started (in June), the IMD had said that the South Peninsula would get less than its normal quota of rain?
Kerala was getting good rain right from the beginning, especially the Western coast.
Was there any unusual pattern of low pressure areas (atmospheric conditions over the Western Ghats that draw in moisture and rain) in and around Kerala?
In August, several low-pressures formed and many of them intensified to become depressions. Whenever they form in the Bay of Bengal, they strengthen the monsoon flow. In Kerala, it is the topography; most of the rains were over the Western Ghats and not in coastal regions like Kollam or Allepey. It was focussed on the hills and all that water went into the rivers.
This has been a year of rains but reportedly the rainfall in Kerala, overall, has been decreasing?
That’s true. Over the last 50 years, monsoon rain over Kerala has been decreasing but that doesn’t rule out such events. (The decrease) is over a long time-scale over decades. In a particular year, it can rain heavily.
However, we’re told that these floods are a once-in-a-century event. Can we expect more, very soon given climate change?
Not only Kerala, but in any part of India, it can happen. Using past data, we have categorically documented that frequency of extreme events are increasing. It can happen anywhere and is part of global warming. There may be other factors too…natural variability, for instance. But this is part of the global warming effect and can happen over Delhi too. Warming means more moisture retention, heightened Westerlies and intense precipitation.
What about factors like urbanisation — Kerala is far more urbanised now than 100 years ago. Can there be heat island-like effects to exacerbate rainfall?
Urbanisation will lead to more intense rain over cities — that’s another well-accepted consequence.
The monsoon deficit (all India) is around 7%. Do you think this will continue for the rest of the season?
Yes, we expect rainfall to be 94-95% of the Long Period Average of 89 cm. The -7 that we’re seeing is surprising because it’s rained heavily everywhere except the northeast. Therefore, this has been a good monsoon, as there was no typical break. In the next three to four days, the monsoon trough will move over to the northeast and those regions will get more rain. This means more rains in Assam, Meghalaya etc.
What is the forecast for Kerala? Have we passed the worst of the season for the State?
Over the next four to five days, there’s no major rain expected in Kerala. Beyond that we can’t be sure. Our extended range forecasts (15 days and ahead) suggest that only north India will be getting more rain. The southern and interior part wont get much rain. The west coast, however, will still see rain — Karnataka, Maharashtra but not really Kerala. I do feel that the worst is over for Kerala.
